Glassing, Roof

Roof Glassed

Posted by Paul

Yesterday I sanded down the starboard side glued strip planks smooth ready for glassing. I had a similar bump where the hard turn problem with the wider planks meets the thin strip planks, as I had on the port side. I attempted to smooth the bump out by adding glue as a filler to gently slope down to the lower plank height but when set and while sanding it down I realised that if it is simply too high and I have to grind it down later I will have to go through the glass whereas if I do as I did on the port side and grind it down now even though it means sanding through the pine veneer to the balsa then it is a safer bet. If it is not then I can bog it back out later but if it is too high, grinding the glass away is not a good option as it would, I imagine weaken the roof and require glass patching. I prefer the piece of mind of knowing the roof glass is not compromised. So I sanded it down to a smooth turn and cleaned the roof off by blowing the dust off and using a damp towel I gave the roof a wipe down and let it dry overnight ready for glassing today.

I effectively had a day off for the Melbourne Cup. So as planned I spent the day glassing the roof. I started the day about 9am by cutting the nidacore to size and fitting it to the roof. I cut the nidacore strip about 5mm wider than it needed to be and bent it into the space and relied on its being slightly oversize to bulge out to the curved shape I needed. It worked a treat. The tightness held it in place and the bulge was almost exactly the curve of the roof. I used some rivets to ensure it did not bulge up too far. I used rivets because they are easy to remove rather than screws which are easy to glass over and become difficult to remove.

nidacore plank in roofnidacore plank in roof 2

I then cut 3 strips of glass the length of the roof. I have decided to glass the roof front to back rather than across the roof. I thought about wether there would be more need for across the boat strength in the roof or fore and aft strength needed and as it is not uni glass I figured in the end that one way is as good as the other and with fore aft strips there would be slightly less joins to fair out later. It also worked out that 3 full widths of glass at 1300mm each and with 100mm overlaps 3 widths of glass worked perfectly. So with everything done it was time to start wetting out the glass. I decided it would be easier to wet the middle strip first then one side then the other would overlap it each side. I rolled out the middle length of glass and mixed up the first batch of ADR (Kinetix) resin, 4:1 by weight. I have a small kitchen scales and measured out 1kg of resin to 250g of hardener into an icecream container and started mixing.

I then simply poured it onto the glass and spread it around with a squeegee. I was going to use a roller but in the end the squeegee works better because as well as spreading the resin it also smoothes down the wet glass to the core, taking out air bubbles and ensuring that the correct amount of resin stays on the glass and excess is squeezed out to another still dry section of glass. I worked out that the roof is 18 square meters and the glass is 657g per square meter so I have 11.8kgs of glass and I used 13kgs of resin, so pretty much exact. The extra kg of resin went to pre soaking the scrim of the nidacore which is necessary for this material or else it sucks the resin down from the wet glass and you get dry glass that is under soaked in resin. So even though I did not do the math until I had finished, it worked out perfectly reassuring me that the glass has the correct resin to glass ratio.

I had to get on the roof to wet the middle strip of glass out starting at the back, standing on the ground and leaning in as far as I could reach, then climbed onto the roof and worked back to the front. Once the first strip was wet out I pre-soaked one sides (port) nidacore with resin and stopped for lunch to let the resin tack off just a little. Half an hour later I rolled the next layer of glass out on the port side, cutting small holes for the rivets and then started wetting it out being very careful over the nidacore not to press too hard and push the core out of its curve as there was nothing underneath to stop me if I pressed to hard but at the same time ensuring the glass was correctly wet out and not too soaked with resin. It all went fine and I had no air bubbles or pools of resin.

I then rolled out the next layer of glass on the port side. The wet nidacore that had tacked off a little held it in place at that point so I smoothed it out over its entire length and repeated the wet out process but this time was able to wet it out from along side the roof and leaning in. So with the second glass strip wet out and the roof 2/3 wet out I simply carried on and finished by wetting out the starboard side layer of glass. The resin on the nidacore was a bit more tacky by this stage so I had to be a little more careful placing the glass as I thought it may stick too much if I needed to lift is and reposition it, fortunately I got it right and could continue on a wet it out.

In all it took me 8 hours today to wet the roof out including a half hour lunch break. I also spent an hour cutting and fitting the nidacore and an hour sanding and cleaning the roof down yesterday. I am sore and tired from working all day crouched under the bridgedeck but extremely pleased. I had the perfect day for wetting out, cool and not humid, the resin did not go off fast which has 2 benefits, firstly the open time was very workable and second no bubbles as it set. I tossed up whether I should bog the glass tomorrow. It will still be green so I could do it but I have decided I will wait to bog it until after I have turned it and glassed the inside. It will be heavy enough to turn over as it is and the roof may flex a little until the frames are back in it upside down to reshape it to the correct shape again but that flexing may crack the bog so better to wait. Once the inside is glassed and set the roof can no longer flex. What I might do tomorrow, while the resin is still green is to add a strip of glass just behind the hard turn in the middle of the roof at the front. It will need to be bogged out so I figure another layer of glass just there will take the place of bog and be stronger. One way or another some height will need to be added just behind so better it has structural strength, for the weight rather than not. Bog does not have any structural strength.

Generally I have given myself a rule on my blog, no religion, no politics. We all may have different opinions on them (and I certainly do) this blog is not the place and I don’t like to offend those with different opinions to me, but I just cant resist today. On the eve of the US Presidential election I really do hope that Barack Obama wins tomorrow. I think the world could do with some hope of change, he has offered an inspirational message, it would also invigorate the idea of racial equality and whilst we don’t get a say, not being American, US foreign policy and the US economy does effect the rest of the world so that’s my 2 cents worth.

After I glass that small strip on in the morning and make sure the rest of the glass is setting properly I will have a couple of days off while I wait for the resin to cure. There are a bunch of other things I could be doing but I think I have earned a short break. I will of course be back on the build on the weekend, preparing to remove the roof from under the bridgedeck to turn it over and glass the inside.

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